Complete program performs SCF-LCAO-MO calculations for both closed and open-shell organic pi-molecules. The Pariser-Parr-People approximations are used with- in the framework of the restricted Hartree-Fock method. The SCF calculation is followed, if desired, by a variational configuration interaction (CI) calculation including singly excited configura- tions.

i) The calculations are restricted to planar molecules.
ii) In order to avoid accumulation of round-off errors, in the iterative procedure, double precision arithmetic is used.
iii) The program is restricted to systems up to about 16 atoms; however the size of the systems can easily be modified if required.

The running time depends on the calculations which are performed (SCF only or SCF+CI). In the SCF part the running time depends strongly on the particular system under consideration, because of the iterative procedure, and also on the accuracy required for the self-consistency. In the CI part the running time depends on the number of configurations which are taken into account in the CI matrix. For example, for a molecule of eight atoms where self-consistency is reached (up to 10(-7)) after about ten iterations and where all singly excited states are in- cluded in the CI calculations, the running time is about two minutes.

i) For systems which have the point group symmetry D2H, the symmetry of excited states is determined and the allowed transitions are then obtained. Moreover the size of the CI matrix is reduced by symmetry. This allows taking account of a great number of configurations and determining directly allowed transitions after CI.
ii) It is possible to choose the types and the number of configurations which are to be included in the CI matrix.

The amount of high speed memory which is needed depends strongly on the size of the system and of the number of configurations retained in the CI matrix. For example for a system of sixteen atoms, with a D2H point group symmetry, a CI calculation including all singly excited states requires 35k words when the overlay structure is used.